文件仅在第一个条件下写入

Question

我正在尝试写入一个文本文件，我的条件是如果该文件中已经存在写入，那么它应该打印“添加了另一行 - 消息”。所以我尝试了以下方法，但它抛出异常'它正在被另一个进程使用'，我可以理解我做错了什么：

public void WriteMessage(string message)
{
   string path = @"C:\Users\AT\Documents\Visual Studio 2013\Projects\Sample_App\Sample_App\app_data\log.txt"; //File path

   FileStream stream;

   if (File.Exists(path))
   {
     stream = new FileStream(path, FileMode.Open, FileAccess.ReadWrite, FileShare.ReadWrite); //This section used to read and write operations

     using (StreamWriter writer = new StreamWriter(stream)) //Writing words to the text file
     {
       string[] lines = File.ReadAllLines(path); //Here is the exception - It's being used by another process

        if (lines.Length > 0)
        {
           writer.WriteLine("\n" + "Another Line Added - " + message);
           writer.Flush();

           stream.Close();
        }
      }
    }
    else
    {
       /**If text file is created for the first time - Starts**/
       stream = new FileStream(path, FileMode.Create); //This section used to read and write operations

       using (StreamWriter writer = new StreamWriter(stream)) //Writing words to the text file
       {
          writer.WriteLine(message);
          writer.Flush();

          stream.Close();
       }
       /**If text file is created for the first time - Ends**/
    }
}

现在会发生什么情况，该文件是为第一个包含文本的 'Hello World!! 创建的，当我向其中添加另一个文本时，我期望得到以下输出：

预期输出：

世界你好！！ ---- 只有第一次否则

添加了另一行 - Hello World！

添加了另一行 - Hello World！

添加了另一行 - Hello World！

我希望有一些想法或建议可以让它发挥作用，并让我知道我做错了什么。这完全是一个简单的。我想在文件中再做一件事，如下所示：

输出：

1) 你好世界！！

2) 你好世界！！

注意：在上面的输出中，每当我运行控制台应用程序时，我都会增加数字。这意味着如果存在相同的写入，那么它应该增加一。我期待一个简单的 Linq 能做到这一点，是否有可能以一种简单的方式做到：（在这种情况下，我是否需要创建任何模型来处理文本文件？）

var query = (var c in fileName
         select c);

foreach(var item in query)
{
  //Do something here
}

我已经完成了以下工作，但还无法完成上述工作：

MSDN - 01

MSDN - 02

Answer 1

File.ReadAllLines(path); 创建另一个流。

将它放在 FileStream 上方应该可以修复它

因为您使用的是using 关键字，所以您不必关闭流

public static void WriteMessage(string message)
    {
        string path = @"log.txt"; //File path

        FileStream stream;

        if (File.Exists(path))
        {
            string[] lines = File.ReadAllLines(path);
            stream = new FileStream(path, FileMode.Open, FileAccess.ReadWrite, FileShare.ReadWrite); //This section used to read and write operations

            using (StreamWriter writer = new StreamWriter(stream)) //Writing words to the text file
            {
                if (lines.Length > 0)
                {
                    writer.WriteLine("\n" + "Another Line Added - " + message);
                    writer.Flush();
                }
            }
        }
        else
        {
            /**If text file is created for the first time - Starts**/
            stream = new FileStream(path, FileMode.Create); //This section used to read and write operations

            using (StreamWriter writer = new StreamWriter(stream)) //Writing words to the text file
            {
                writer.WriteLine(message);
                writer.Flush();
            }
            /**If text file is created for the first time - Ends**/
        }
    }

Answer 2

处理原始流是一种有效的文件处理方式，如果您及时返回的话。我们有更新的 .NET Framework 版本和更简单更好的文件处理功能：

public void WriteMessage(string message)
{
   string path = @"C:\Users\AT\Documents\Visual Studio 2013\Projects\Sample_App\Sample_App\app_data\log.txt"; //File path

   if (File.Exists(path))
   {
     File.AppendAllLines(path, new[]{ "Another line added - Hello world" });
   }
   else
   {
     File.AppendAllLines(path, new[]{ "Hello World!!" });
   }
}

实际考虑文件内容的示例：

public void WriteMessageWithLineNumbers(string message)
{
   string path = @"C:\Users\AT\Documents\Visual Studio 2013\Projects\Sample_App\Sample_App\app_data\log.txt"; //File path

   if (File.Exists(path))
   {
     var lines = File.ReadAllLines(path);

     var nextLine = string.Format("{0} - Hello World", lines.Length + 1)

     File.AppendAllLines(path, new[]{ nextLine });
   }
   else
   {
     File.AppendAllLines(path, new[]{ "1 - Hello World!!" });
   }
}

Answer 3

StreamWriter 用于文本写入不需要构造函数的Stream 参数。它可以直接使用文件本身的路径。这样就可以省略FileStream:

    public static void WriteMessage(string message)
    {
        var path = @"../../sth.txt"; //File path
        if (File.Exists(path))
        {
            string[] lines = File.ReadAllLines(path);//This section used to read and write operations
            using (var writer = new StreamWriter(path, true)) //Writing words to the text file
            {
                if (lines.Length > 0)
                {
                    writer.WriteLine("Another Line Added - " + message);
                }
                else
                {
                    writer.WriteLine(message);
                }

                writer.Flush();
            }
        }
        else
        {
            /**If text file is created for the first time - Starts**/
            using (StreamWriter writer = new StreamWriter(path)) //Writing words to the text file
            {
                writer.WriteLine(message);
                writer.Flush();
            }
            /**If text file is created for the first time - Ends**/
        }
    }